EP3273237B1 - Method and measuring device for determining physical gas properties - Google Patents

Description

The invention relates to a method and a measuring device for determining physical properties and combustion-relevant variables of gases and gas mixtures. Physical gas properties are understood to mean, in particular, the density, thermal conductivity, heat capacity and viscosity and the combustion-relevant variables that can be correlated therefrom, such as the energy content, calorific value, Wobbe index, the methane number and/or the air requirement of the gas or gas mixture.

With gas combustion controls, it is important to keep the burner load constant when the quality of the fuel gas changes. The corresponding index to indicate the interchangeability of gases is the Wobbe index, formed from the calorific value and the square root of the density ratio between air and this gas. With the same Wobbe index, the same heat load on a burner results.

When controlling (natural) gas engines, knowledge of the calorific value of changing (natural) gas qualities is important in order to increase performance and efficiency; however, the methane number, which is analogous to the octane number for gasoline, is used to assess ignition behavior (knocking or misfiring) for gas used.

For an optimal combustion process, the correct mixing ratio between fuel gas and air is important, the so-called air requirement. If there is not enough air, soot (exhaust gases) usually forms, which can lead to the destruction of fuel cells, especially. Too much air during combustion results in lower power output. The optimal value depends on the respective application, but changes again as the gas quality changes.

1. A. Dielektrizitätskonstante, Schallgeschwindigkeit, CO₂-Gehalt
2. B. Schallgeschwindigkeit bei 2 Drücken, CO₂-Gehalt
3. C. Wärmeleitfähigkeit bei 2 Temperaturen, Schallgeschwindigkeit
4. D. Wärmeleitfähigkeit, Wärmekapazität, dynamische Viskosität
5. E. Wärmeleitfähigkeit, Infrarot Absorption (nicht dispersiv)
6. F. Infrarot Absorption (dispersiv)

Correlation methods for calculating variables relevant to combustion technology are known from the literature, see for example U. Wernekinck, “Gas measurement and gas billing”, Vulkan Verlag, 2009, ISBN 978-3-8027-5620-7 . The following combinations of measurement variables are used:

1. A. Dielectric constant, speed of sound, CO ₂ content
2. B. Speed of sound at 2 pressures, CO ₂ content
3. C. Thermal conductivity at 2 temperatures, speed of sound
4. D. Thermal conductivity, heat capacity, dynamic viscosity
5. E. Thermal conductivity, infrared absorption (non-dispersive)
6. F. Infrared absorption (dispersive)

There are currently only a few commercially available devices that are approved for calorific value measurements, e.g. the EMC500 device from RMG-Honeywell (type D plus CO ₂ content), or the Gas-lab Q1 device from Elster-Instromet (type E plus _CO2 concentration). However, due to the high purchase price, none of these devices are suitable for the mass market.

Integrated CMOS hot wire anemometers enable both microthermal thermal conductivity measurement and Mass flow measurement. This technology is discussed D. Matter, B. Kramer, T. Kleiner, B. Sabbattini, T. Suter, "Microelectronic household gas meter with new technology", Technisches Messen 71, 3 (2004), pp. 137-146 pointed out. It differs in particular from conventional thermal mass flow meters in that it measures directly in the gas stream and not from outside on a metal capillary surrounding the gas stream.

In WO 99/02964 A1 A method for determining the density of a gas is described, in which the gas flows from a container through a critical nozzle and the time Δt for a specific pressure drop is measured.

In EP 0 591 639 A2 A method and a device for determining the gas density are described, whereby the gas density is first measured under given conditions and then the gas density under flow conditions is determined using a volume correction ratio.

Out of EP 2 015 056 A1 a thermal flow sensor is known for determining a variable relevant to combustion technology, based on a thermal conductivity measurement with a quasi-known mass flow. For this purpose, a critical nozzle is used to keep the mass flow constant and an attempt is made to correct the gas type dependence of the critical nozzle using thermal conductivity. However, the information on the correlation of variables relevant to combustion technology is limited to two quasi-independent measured values, so that no validation of the measurement data is possible.

Out of WO 2004/036209 A1 a sensor is known for determining variables relevant to combustion technology, in which the mass flow is kept constant and a quantity proportional to the heat capacity is determined by means of a thermal measurement. Since it is not a microthermal sensor, the thermal conductivity cannot be determined, which means that the determination of the heat capacity and the combustion-relevant variables derived from it is only possible up to a proportionality factor, which makes additional calibration with known gas compositions necessary. In addition, information about thermal conductivity and thus the possibility of this are no longer available Correlation of the thermal conductivity λ with one of the combustion-relevant quantities. Furthermore, the accuracy of this method is limited by the changes that occur in the inaccessible thermal conductivity λ.

The invention is therefore based on the object of specifying a method and a measuring device for determining physical properties of gases and gas mixtures, with which a higher level of accuracy can be achieved than with the sensors from the patent documents described above, whereby it is possible to use the measuring device deeper Costs to produce than commercially available devices that are approved for calibration-required calorific value measurements.

The object is achieved by a method according to claim 1 and by a measuring device according to claim 6.

Pressure drop measurement of a given volume of gas through a critical nozzle:

worin C_d den "Discharge Coefficient", d.h. den Verlustfaktor einer realen gegenüber einer idealen kritischen Düse, p den Vordruck, A* den Düsenquerschnitt, T die Vortemperatur, R_m die universelle Gaskonstante, M das Molekulargewicht des Gases und ψ_max den Maximalwert der Ausflussfunktion bezeichnet. Letztere ist eine Funktion des isentropen Koeffizienten γ = c_p /c_V (Verhältnis von isobarer zu isochorer Wärmekapazität), $$\psi =\sqrt{\gamma }\cdot {\left(\frac{\gamma +1}{2}\right)}^{\frac{\gamma +1}{2\left(1-\gamma \right)}}.$$

The mass flow ṁ through a critical nozzle is given by $$\dot{m}=C_d\cdot p\cdot A*\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{M}{T\cdot R_m}},$$

where C _d is the "Discharge Coefficient", ie the loss factor of a real versus an ideal critical nozzle, p the pre-pressure, A * the nozzle cross-section, T the pre-temperature, R _m the universal gas constant, M the molecular weight of the gas and ψ _max the maximum value of the called outflow function. The latter is a function of the isentropic coefficient γ = c _p / c _V (ratio of isobaric to isochoric heat capacity), $$\psi =\sqrt{\gamma }\cdot {\left(\frac{\gamma +1}{2}\right)}^{\frac{\gamma +1}{2\left(1-\gamma \right)}}.$$

If the gas from a known volume V is allowed to expand from a high pressure via the critical nozzle (e.g. from 9 to 4 bar), the pressure in the volume depends on the time t as follows due to the ideal gas law: $$p\left(t\right)=m\left(t\right)\cdot \frac{R_m\cdot T}{M\cdot v}.$$

und zusammen mit Gleichung (1) zu $$\begin{array}{c}\frac{\mathit{dp}\left(t\right)}{\mathit{dt}}=C_d\cdot p\cdot A^{*}\cdot {\psi }_{\max }\cdot \sqrt{\frac{M}{T\cdot R_m}}\cdot \frac{R_m\cdot T}{M\cdot V}\\ =C_d\cdot \frac{A*\cdot {\psi }_{\max }}{V}\cdot \sqrt{\frac{R_m\cdot T}{M}}\cdot p\left(t\right)\end{array}$$

The rate of change of the pressure is therefore: $$\frac{\mathit{dp}\left(t\right)}{\mathit{German}}=\frac{\mathit{dm}\left(t\right)}{\mathit{German}}\cdot \frac{R_m\cdot T}{M\cdot v}=\dot{m}\left(t\right)\cdot \frac{R_m\cdot T}{M\cdot v}$$

and together with equation (1) to $$\begin{array}{c}\frac{\mathit{dp}\left(t\right)}{\mathit{German}}=C_d\cdot p\cdot A^{*}\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{M}{T\cdot R_m}}\cdot \frac{R_m\cdot T}{M\cdot v}\\ =C_d\cdot \frac{A*\cdot {\psi }_{\mathrm{Max}}}{v}\cdot \sqrt{\frac{R_m\cdot T}{M}}\cdot p\left(t\right)\end{array}$$

If you measure the course of the pressure as a function of time, you can determine the time constant τ of the associated exponential function obtained through integration: $$1/\tau =\frac{C_d\cdot A*\cdot {\psi }_{\mathrm{Max}}}{v}\cdot \sqrt{\frac{R_m\cdot T}{M}}.$$

definieren.If you also know the temperature T by measuring, you can create a gas property factor by omitting all non-gas-dependent variables $$\mathrm{\Gamma }*:=C_d\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{1}{M}}$$

define.

wobei in diesem Fall der Druck vor der Düse, p_Nozzle, konstant ist, was zu einem mit der Zeit linearen Druckanstieg im Volumen V führt mit $$\frac{C_d\cdot A*\cdot {\psi }_{\max }}{V}\cdot \sqrt{\frac{R_m\cdot T}{M}}\cdot p_{\mathit{Nozzle}}$$

als Proportionalitätskonstante. Kennt man durch Messen zusätzlich die Temperatur T und den Düsenvordruck p_Nozzle, kann man durch Weglassen aller nicht gasabhängigen Grössen wiederum den Gaseigenschaftsfaktor $$\mathrm{\Gamma }*:=C_d\cdot {\psi }_{\max }\cdot \sqrt{\frac{1}{M}}$$

definieren.Conversely, if the gas is allowed to expand from a higher pressure via the critical nozzle into a known volume V (e.g. from ambient pressure to vacuum), equation (5') for the pressure increase in the volume is as follows: $$\begin{array}{c}\frac{\mathit{dp}\left(t\right)}{\mathit{German}}=C_d\cdot p_{\mathit{Nozzle}}\cdot A*\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{M}{T\cdot R_m}}\cdot \frac{R_m\cdot T}{M\cdot v}\\ =C_d\cdot \frac{A*\cdot {\psi }_{\mathrm{Max}}}{v}\cdot \sqrt{\frac{R_m\cdot T}{M}}\cdot p_{\mathit{Nozzle}}\end{array},$$

where in this case the pressure in front of the nozzle, p _Nozzle , is constant, which leads to a linear increase in pressure in the volume V over time $$\frac{C_d\cdot A*\cdot {\psi }_{\mathrm{Max}}}{v}\cdot \sqrt{\frac{R_m\cdot T}{M}}\cdot p_{\mathit{Nozzle}}$$

as a proportionality constant. If you also know the temperature T and the nozzle pre-pressure p _Nozzle by measuring, you can get the gas property factor again by omitting all non-gas-dependent variables $$\mathrm{\Gamma }*:=C_d\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{1}{M}}$$

define.

Mass flow measurement using microthermal sensors:

wobei
v_x   die Komponente der mittleren Fliessgeschwindigkeit (Geschwindigkeitsvektor) v in x-Richtung, d. h. entlang des Gasstromes,
T  die Temperatur,
$\frac{d}{\mathit{dx}}T$

  der Temperaturgradient,
c_p   die Wärmekapazität des Gases bei konstantem Druck,
ρ  die Dichte,
λ  die Wärmeleitfähigkeit des Gases,
∇² T  der Laplace-Operator, angewandt auf die Temperatur T, wobei $${\nabla }^2={\left(\frac{d}{d_x}\right)}^2+{\left(\frac{d}{\mathit{dy}}\right)}^2+{\left(\frac{d}{\mathit{dz}}\right)}^2,$$

bedeuten. Da das Gas (Gasstrom) nur in x-Richtung fliesst, werden die Komponenten v_y bzw. v_z in y-Richtung bzw. in z-Richtung der mittleren Fliessgeschwindigkeit v zu Null angenommen. Θ mit der Einheit Watt/m³ beschreibt den Quellterm des Heizelements. Der Quellterm rührt bei der mikrothermischen Methode vom Heizdraht eines miniaturisierten, integrierten Hitzdrahtanemometers her, der Wärmeenergie in das System speist. Die Lösung der Gleichung (8), die die Temperaturverteilung im mikrothermischen System beschreibt, erlaubt es, durch das Messen dieser Temperaturverteilung den Faktor S, $$S:=\frac{c_p}{\lambda }\cdot \rho \cdot {\mathrm{v}}_{\mathrm{x}}=\frac{c_p}{\lambda }\cdot \frac{\dot{m}}{A},$$

zu bestimmen, wobei A den Querschnitt des Flusskanals über dem mikrothermischen Sensor bezeichnet. In Kombination mit der kritischen Düse, d.h. durch Anordnen des mikrothermischen Sensors nach der kritischen Düse, ist der Massenfluss aber durch Gleichung (1) gegeben, weswegen $$\frac{c_p}{\lambda }\cdot \rho \cdot {\nu }_x=\frac{c_p}{\lambda }\cdot C_d\cdot p\cdot \frac{A^{*}}{A}\cdot {\psi }_{\max }\cdot \sqrt{\frac{M}{T\cdot R_m}}.$$

To describe the microthermal mass flow measurement, the one-dimensional heat conduction equation describing the microthermal system is assumed ( Kerson Huang: Statistical Mechanics, 2nd edition, John Wiley & Sons, New York 1987, ISBN 0-471-85913-3 ): $$\frac{c_p}{\lambda }\cdot \rho {\mathrm{v}}_{\mathrm{x}}\cdot \frac{d}{\mathit{dx}}T={\nabla }^{2}T+\frac{1}{\lambda }\mathrm{\Theta },$$

where
v _x the component of the mean flow velocity (velocity vector) v in the x direction, ie along the gas flow,
T is the temperature,
$\frac{d}{\mathit{dx}}T$

the temperature gradient,
c _p is the heat capacity of the gas at constant pressure,
ρ the density,
λ is the thermal conductivity of the gas,
∇ ² T the Laplace operator applied to the temperature T , where $${\nabla }^2={\left(\frac{d}{d_x}\right)}^2+{\left(\frac{\mathrm{<figure-callout\; id="2"\; label="d\; dy"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}{\mathit{dy}}\right)}^2+{\left(\frac{d}{\mathit{currently}}\right)}^2,$$

mean. Since the gas (gas stream) only flows in the x direction, the components v _y and v _z in the y direction and in the z direction, respectively, become the average flow velocity v assumed to be zero. Θ with the unit Watt/m ³ describes the source term of the heating element. The source term comes from the microthermal method from the heating wire of a miniaturized, integrated hot-wire anemometer, which feeds thermal energy into the system. The solution to equation (8), which describes the temperature distribution in the microthermal system, allows the factor S, by measuring this temperature distribution, $$S:=\frac{c_p}{\lambda }\cdot \rho \cdot {\mathrm{v}}_{\mathrm{x}}=\frac{c_p}{\lambda }\cdot \frac{\dot{m}}{A},$$

to determine, where A denotes the cross section of the flow channel above the microthermal sensor. In combination with the critical nozzle, ie by arranging the microthermal sensor after the critical nozzle, the mass flow is given by equation (1), which is why $$\frac{c_p}{\lambda }\cdot \rho \cdot {\nu }_x=\frac{c_p}{\lambda }\cdot C_d\cdot p\cdot \frac{A^{*}}{A}\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{\frac{M}{T\cdot R_m}}.$$

By measuring pressure p and temperature T and again by omitting all gas-independent variables, a second gas property factor is obtained $$\mathrm{\Gamma }=\frac{c_p}{\lambda }\cdot C_d\cdot {\psi }_{\mathrm{Max}}\cdot \sqrt{M}.$$

The omission of all gas-independent quantities in equations (7) and (11) occurs implicitly when one sets Γ and Γ* in relation to Γ and Γ* of a known (calibration) gas. See also Fig. 4 .

Measurement of thermal conductivity using a microthermal sensor:

Note that the thermal conductivity λ also has a separate effect on the solution of equation (8) because of the swelling term Θ. Conversely, thermal conductivity can be determined using the microthermal sensor is measured without applied mass flow ( v _x =0 or ṁ = 0). The associated differential equation for the temperature distribution is then simple $${\nabla }^{2}T=-\frac{1}{\lambda }\mathrm{\Theta }\mathrm{.}$$

Validation of the gas property factors Γ or Γ*:

da das Molekulargewicht wegen des für die meisten Gase praktisch identischen Molvolumens proportional zur Normdichte (Dichte bei Normbedingungen 1013.25 mbar und 273.15 K) ist. Damit kann aus dem mittels mikrothermischen Sensors gemessenen Faktor S in Gleichung (9) die Fliessgeschwindigkeit v_x und zusammen mit dem Flusskanalquerschnitt A der Normvolumenfluss φ_norm = v_x · A extrahiert werden. Integration dieses Volumenflusses über die Zeit, d.h. im Zeitintervall t₂ -t₁ , sollte dann mit dem aus den entsprechenden Druck- und Temperaturwerten berechneten, abgeflossenen Gasvolumen übereinstimmen: $${\displaystyle \underset{t_1}{\overset{t_2}{\int }}{\varphi }_{\mathit{norm}}\left(t\right)\mathit{dt}\stackrel{!}{=}\frac{\left(p\left(t_2\right)-p\left(t_1\right)\right)}{1013.25\mathit{mbar}}\cdot \frac{273.15K}{T}\cdot V}.$$

The ratio of the two gas property factors Γ and Γ* gives $$\raisebox{1ex}{$\mathrm{\Gamma }$}\!\left/ \!\raisebox{-1ex}{${\mathrm{\Gamma }}^{*}$}\right.=\frac{c_p}{\lambda }\cdot M\propto \frac{c_p}{\lambda }\cdot {\rho }_{\mathit{standard}},$$

because the molecular weight is proportional to the standard density (density under standard conditions 1013.25 mbar and 273.15 K) because of the practically identical molar volume for most gases. _This means that _the flow velocity _v Integration of this volume flow over time, ie in the time interval t ₂ - t ₁ , should then correspond to the gas volume flown calculated from the corresponding pressure and temperature values: $${\displaystyle \underset{t_1}{\overset{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}{\int }}{\varphi }_{\mathit{standard}}\left(t\right)\mathit{German}\stackrel{!}{=}\frac{\left(\mathrm{<figure-callout\; id="2"\; label="p\; t"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}\left(t_{}\right)\left({}_2\right)-\mathrm{<figure-callout\; id="1"\; label="p\; t"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}\left(t_{}\right)\left({}_1\right)\right)}{1013.25\mathit{mbar}}\cdot \frac{273.15K}{T}\cdot v}.$$

If the two values do not match, depending on which quantity can be measured less precisely, the standard volume flow or the pressure signal can be corrected until equation (14) is fulfilled. In the case of a standard volume flow correction for ν _x = φ _norm / A , the right-hand side of equation (13) learns about the measured factor S in equation (9) also a correction and thus also the gas property factor Γ again via equation (13). In the case of a pressure signal correction, a corrected time constant τ follows in equation (6) or a corrected proportionality constant in equation (6') and thus a correction of the gas property factor Γ* in equation (7) or (7'). In this way, Γ and Γ* have been determined consistently because the mass flow through the nozzle is the same as the mass flow applied to the microthermal sensor.

Correlation of variables relevant to combustion technology:

With the measurements of the gas property factors Γ and Γ* as well as the thermal conductivity λ, three independent measurement variables are available with which quantities Q relevant to combustion can now be correlated using a function f _corr : $$Q_{\mathit{corr}}={ƒ}_{\mathit{corr}}\left(\mathrm{\Gamma },{\mathrm{\Gamma }}^{*},\lambda \right).$$

mit Exponenten r = -0.2, s = -1.8 und t = -0.2 und einem typischen H-Erdgas als Referenz.For example, the correlation of the in Fig. 4 shown density ratio ρ _corr / ρ _ref at 0°C and 1013.25 mbar the following correlation function: $$\raisebox{1ex}{${\rho }_{\mathit{corr}}$}\!\left/ \!\raisebox{-1ex}{${\rho }_{\mathit{ref}}$}\right.={ƒ}_{\mathit{corr}}\left(\mathrm{\Gamma },{\mathrm{\Gamma }}^{*},\lambda \right)={\mathrm{\Gamma }}^r\cdot {\mathrm{\Gamma }}^{*s}\cdot {\lambda }^t$$

with exponents r = -0.2, s = -1.8 and t = -0.2 and a typical H natural gas as a reference.

Method and measuring device according to the present invention

• fliesst das Gas oder Gasgemisch aus einem Gasreservoir durch eine kritische Düse und über einen mikrothermischen Sensor, wobei die kritische Düse und der mikrothermischen Sensor mit demselben Massenfluss beaufschlagt werden;
• wobei der Druckabfall im Gasreservoir als Funktion der Zeit gemessen wird;
• aus den Messwerten des Druckabfalls ein erster, von einer ersten Gruppe von physikalischen Eigenschaften des Gases oder Gasgemisches abhängiger Gaseigenschaftsfaktor F* bestimmt wird, wobei der erste Gaseigenschaftsfaktor aus einer Zeitkonstante des Druckabfalls abgeleitet und von einem exponentiellen Abfall des gemessenen Druckes ausgegangen wird;
• aus dem Durchflusssignal des mikrothermischen Sensors ein zweiter, von einer zweiten Gruppe von physikalischen Eigenschaften des Gases oder Gasgemisches abhängiger Gaseigenschaftsfaktor Γ bestimmt wird, wobei der zweite Gaseigenschaftsfaktor zum Beispiel die Wärmekapazität c_p des Gases oder Gasgemisches enthält oder von derselben abhängig ist;
• mit Hilfe des mikrothermischen Sensors die Wärmeleitfähigkeit λ des Gases oder Gasgemisches bestimmt wird; und
• aus dem ersten und/oder zweiten Gaseigenschaftsfaktor F*, Γ und der Wärmeleitfähigkeit λ mittels Korrelation eine gesuchte physikalische Eigenschaft oder brenntechnisch relevante Grösse ermittelt wird.

In the method for determining physical properties and/or combustion-relevant variables of a gas and gas mixture according to the present invention:

• the gas or gas mixture flows from a gas reservoir through a critical nozzle and over a microthermal sensor, the critical nozzle and the microthermal sensor being subjected to the same mass flow;
• wherein the pressure drop in the gas reservoir is measured as a function of time;
• a first gas property factor F*, which is dependent on a first group of physical properties of the gas or gas mixture, is determined from the measured values of the pressure drop, the first gas property factor being derived from a time constant of the pressure drop and an exponential drop in the measured pressure being assumed;
• a second gas property factor Γ, which is dependent on a second group of physical properties of the gas or gas mixture, is determined from the flow signal of the microthermal sensor, the second gas property factor containing, for example, the heat capacity c _p of the gas or gas mixture or being dependent on the same;
• the thermal conductivity λ of the gas or gas mixture is determined with the help of the microthermal sensor; and
• A desired physical property or combustion-relevant quantity is determined from the first and/or second gas property factor F*, Γ and the thermal conductivity λ by means of correlation.

An exponential drop in the measured pressure is assumed and the first gas property factor Γ* is derived from the time constant of the pressure drop, the first gas property factor being formed, for example, by additionally measuring the temperature T and omitting all non-gas-dependent variables.

The pressure in the gas reservoir at the beginning of the pressure drop measurement is typically greater than the critical pressure p _crit of the critical nozzle and the external pressure after the critical nozzle is less than half of the critical pressure, or the pressure in the gas reservoir at the beginning of the pressure increase measurement is typically less than half the critical pressure p _crit of the critical nozzle and the pressure in front of the critical nozzle is greater than the critical pressure. Regardless of the embodiment and variant, the gas reservoir is typically separated from the gas supply during the measurement. The volume of the gas reservoir is advantageously chosen so that the pressure in the gas reservoir decreases or increases significantly by the end of the measurement, for example by at least a tenth or fifth of the original pressure.

Furthermore, the invention also includes the use of a gas reservoir and a critical nozzle for determining physical properties and/or combustion-relevant variables of a gas or gas mixture, wherein the gas or gas mixture flows under pressure from the gas reservoir through the critical nozzle, with the pressure drop in the gas reservoir as Function of time is measured, from the measured values of the pressure drop a gas property factor Γ* which is dependent on physical properties of the gas or gas mixture is determined, which is derived from a time constant of the pressure drop, and from the gas property factor Γ* by means of correlation a desired physical property or one relevant to combustion technology is determined Size is determined.

In another advantageous embodiment, a negative pressure is generated in the gas reservoir, and the gas or gas mixture flows under pressure through the critical nozzle into the gas reservoir, the pressure increase in the gas reservoir being measured as a function of time and from the measured values of the pressure increase based on physical properties of the gas or gas mixture-dependent gas property factor F* is determined, from which a desired physical property or combustion-relevant variable is determined by means of correlation.

The above-described use of a gas reservoir and a critical nozzle for determining physical properties and/or combustion-relevant variables of a gas or gas mixture or the corresponding method in which a gas reservoir and a critical nozzle for determining physical properties and/or combustion-relevant variables of a gas or Gas mixtures are used can also be viewed as an independent invention, which can additionally include a measuring device with an evaluation unit, gas reservoir and critical nozzle, the evaluation unit for the use of the gas reservoir and the critical nozzle to determine physical properties and / or combustion-relevant quantities of a gas or gas mixture or is set up to carry out the corresponding process.

Further advantages can be seen from the description below.

Fig. 1a

ein Ausführungsbeispiel des schematischen Aufbaus einer Messvorrichtung gemäss eines Beispiels, welches nicht Teil der Erfindung ist, (Hochdruckvariante),

Fig. 1b

eine Ausführungsvariante zu dem in Fig. 1a gezeigten Beispiels, welches nicht Teil der Erfindung ist,

Fig. 2

ein zweites Ausführungsbeispiele des schematischen Aufbaus einer Messvorrichtung gemäss eines Beispiels, welches nicht Teil der Erfindung ist, (Niederdruckvariante),

Fig. 3

ein Ausführungsbeispiel eines mikrothermischen Sensors zur Verwendung in einer Messvorrichtung gemäss eines Beispiels, welches nicht Teil der Erfindung ist, und

Fig. 4

eine grafische Darstellung des direkt gemessenen Dichteverhältnisses (y-Achse) in Abhängigkeit des korrelierten Dichteverhältnisses (x-Achse) für verschieden Gasgruppen bei Normbedingungen (0°C, 1013.25 mbar).

Fig. 5a

ein Ausführungsbeispiel des schematischen Aufbaus einer Messvorrichtung gemäss einer zweiten Ausführungsform der Erfindung (Hochdruckvariante),

Fig. 5b

eine Ausführungsvariante zu dem in Fig. 5a gezeigten Ausführungsbeispiel,

Fig. 6

ein zweites Ausführungsbeispiele des schematischen Aufbaus einer Messvorrichtung gemäss der zweiten Ausführungsform der Erfindung (Niederdruckvariante),

Fig. 7

eine grafische Darstellung des direkt gemessenen Methananteils (y-Achse) in Abhängigkeit des korrelierten Methananteils (x-Achse) für ein binäres Rohbiogas (Methan und Kohlendioxid).

Fig. 8a

ein Ausführungsbeispiel des schematischen Aufbaus einer Messvorrichtung gemäss eines Beispiels, welches nicht Teil der Erfindung ist, mit Gasreservoir und mikrothermischem Sensor (Hochdruckvariante),

Fig. 8b

eine Ausführungsvariante zu dem in Fig. 8a gezeigten Ausführungsbeispiel,

Fig. 9

ein zweites Ausführungsbeispiele des schematischen Aufbaus einer Messvorrichtung gemäss eines Beispiels, welches nicht Teil der Erfindung ist, mit Gasreservoir und mikrothermischem Sensor (Niederdruckvariante),

Fig. 10

eine grafische Darstellung der Klasseneinteilung von Erdgasgemischen anhand der Wärmediffusivität (y-Achse) bei gleichzeitiger Kenntnis der Wärmeleitfähigkeit λ (x-Achse).

The invention is explained in more detail below with reference to the drawings. Show it:

Fig. 1a

an exemplary embodiment of the schematic structure of a measuring device according to an example which is not part of the invention (high-pressure variant),

Fig. 1b

an embodiment variant to the one in Fig. 1a example shown, which is not part of the invention,

Fig. 2

a second exemplary embodiment of the schematic structure of a measuring device according to an example which is not part of the invention (low-pressure variant),

Fig. 3

an embodiment of a microthermal sensor for use in a measuring device according to an example which is not part of the invention, and

Fig. 4

a graphical representation of the directly measured density ratio (y-axis) as a function of the correlated density ratio (x-axis) for different gas groups at standard conditions (0°C, 1013.25 mbar).

Fig. 5a

an exemplary embodiment of the schematic structure of a measuring device according to a second embodiment of the invention (high-pressure variant),

Fig. 5b

an embodiment variant to the one in Fig. 5a shown embodiment,

Fig. 6

a second exemplary embodiment of the schematic structure of a measuring device according to the second embodiment of the invention (low-pressure variant),

Fig. 7

a graphical representation of the directly measured methane content (y-axis) as a function of the correlated methane content (x-axis) for a binary raw biogas (methane and carbon dioxide).

Fig. 8a

an embodiment of the schematic structure of a measuring device according to an example, which is not part of the invention, with gas reservoir and microthermal sensor (high-pressure variant),

Fig. 8b

an embodiment variant to the one in Fig. 8a shown embodiment,

Fig. 9

a second exemplary embodiment of the schematic structure of a measuring device according to an example, which is not part of the invention, with a gas reservoir and microthermal sensor (low-pressure variant),

Fig. 10

a graphical representation of the classification of natural gas mixtures based on the thermal diffusivity (y-axis) with simultaneous knowledge of the thermal conductivity λ (x-axis).

Fig. 1a shows an exemplary embodiment of the schematic structure of a measuring device according to the present invention in the case in which the gas main line 1 has a pressure that is higher than the critical pressure for the critical nozzle 6 of the measuring device (high-pressure variant). In the exemplary embodiment, the measuring device comprises, in addition to the critical nozzle 6, an evaluation unit 11, which is set up to carry out a method according to the present invention, a gas reservoir 4, which is provided with a pressure sensor 8, and a microthermal sensor 7 for measuring the flow and thermal conductivity, wherein the gas reservoir 4 is connected to the critical nozzle 6 and the microthermal sensor 7 for the measurement.

If necessary, the measuring device can additionally contain one or more of the following components: a measuring line 2, which leads to the gas reservoir 4, and which can be connected to a main gas line 1 during operation, an inlet valve 3, which can be arranged in the measuring line 2, in order to to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir, in order to control the gas flow from the gas reservoir, an outlet 10, in order to remove the gas flowing out of the measuring device, an additional pressure sensor 8 ', which is at the outlet 10 can be arranged, a temperature sensor 9, which is arranged in the gas reservoir, and a compressor 12 ', which can be arranged on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

An exemplary embodiment, which is not part of the invention, is described below with reference to Fig. 1a described. In the method, the gas or gas mixture flows from the gas reservoir 4 through the critical nozzle 6 and over the microthermal sensor 7, with the critical nozzle and the microthermal sensor being subjected to the same mass flow. The pressure drop in the gas reservoir 4 is measured as a function of time and a first gas property factor Γ*, which is dependent on a first group of physical properties of the gas or gas mixture, is determined from the measured values of the pressure drop, the first gas property factor being derived, for example, from a time constant of the pressure drop . From the flow signal of the microthermal sensor 7, a second gas property factor Γ, which is dependent on a second group of physical properties of the gas or gas mixture, is determined, the second gas property factor containing, for example, the heat capacity c _p of the gas or gas mixture or being dependent on the same. Furthermore, with the help of the microthermal sensor 7, the thermal conductivity λ of the gas or gas mixture is determined and a desired physical property or combustion-relevant quantity is determined from the first and/or second gas property factor Γ*, Γ and the thermal conductivity λ by means of correlation.

Further advantageous embodiments and variants of the method can be found in previous sections of the description. The description below provides additional details about the procedure that can be used if necessary.

Advantageously, the inlet valve 3 and outlet valve 5 are first opened in order to allow the gas or gas mixture to be measured to flow from the main gas line 1 via the measuring line 2 through the measuring device, which can ensure that there is no longer any foreign gas from the last measurement in the measuring device . The inlet valve and outlet valve can be opened via a control unit. In some cases, the evaluation unit 11 can also be used, as in Fig. 1a shown, take over control of the inlet valve and exhaust valve. Then it will be the outlet valve 5 is closed and the gas reservoir 4, whose volume V is known, fills until the inlet valve 3 is closed. Pressure p and temperature T in the gas reservoir can be measured with the pressure sensor 8 or temperature sensor 9, so that the standard volume V _norm of the gas or gas mixture located in the gas reservoir 4 can be determined at any time. $$v_{\mathit{standard}}=\frac{p}{1013.25\mathit{mbar}}\cdot \frac{273.15K}{T}\cdot v.$$

If the pressure p in the gas reservoir 4 is greater than the pressure p _crit , which is required so that the nozzle 6 can be operated critically, the outlet valve 5 can be opened again. Preferably, the pressure p in the gas reservoir is several bar higher than p _crit , so that the pressure drop measurement can be carried out over this range of pressure increase without the nozzle 6 no longer being operated critically. Now the outlet valve 5 is closed again, which ends the pressure drop measurement. The pressure sensor 8 is preferably designed as a differential pressure sensor relative to the outlet 10 of the measuring device. However, it is also possible to provide an additional pressure sensor 8' at the outlet.

During the pressure drop measurement, the time-dependent pressure p(t) and the time-dependent temperature T(t) in the pressure reservoir 4 were measured and recorded by the evaluation unit 11. With this data, the time constant τ in equation (6) or the gas property factor Γ* in equation (7) is determined in the evaluation unit. At the same time, flow data was measured with the microthermal sensor 7, which in turn was recorded by the evaluation unit in order to determine the factor S in equation (9) or the gas property factor Γ in equation (11). Since the inlet and outlet valves are closed after the pressure drop measurement, gas no longer flows through the microthermal sensor 7. The thermal conductivity measurement λ can now be measured. Again recorded by the evaluation unit, the thermal conductivity λ is determined using the solution to equation (12).

The (optional) validation of the gas property factor Γ or Γ* now takes place in the evaluation unit 11 and then, depending on the desired combustion-relevant quantity Q, its calculation using equation (15) with the previously determined correlation function Q _corr = f _corr (Γ, Γ*, λ ).

If necessary, you can also, as in Fig. 1b shown, a compressor 12 'may be provided, which is arranged, for example, on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

Fig. 2 shows a second exemplary embodiment of the schematic structure of a measuring device, which is not part of the invention, in which a negative pressure is used in the gas reservoir. This so-called low-pressure variant is advantageous, for example, when supplying gas to end customers. In the second exemplary embodiment, the measuring device comprises, in addition to the gas reservoir 4, a pressure sensor 8 with which the gas reservoir is provided, an evaluation unit 11 which is set up to carry out a method according to the present invention, a critical nozzle 6, and a microthermal sensor 7 for measuring the flow and the thermal conductivity, the gas reservoir 4 being connected to the critical nozzle 6 and the microthermal sensor 7 for the measurement.

If necessary, the measuring device can additionally contain one or more of the following components: a vacuum pump 12, which is connected to the gas reservoir 4 in order to generate a negative pressure in the gas reservoir, a measuring line 2, which leads to the gas reservoir 4, and which, in operation, with a Main gas line 1 can be connected, an inlet valve 3, which can be arranged in the measuring line 2 in order to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir in order to control the gas flow from the gas reservoir, an outlet 10 to remove the gas flowing out of the measuring device, an additional pressure sensor 8 ', which can be arranged in the measuring line 2 or gas main line, and a temperature sensor 9, which is arranged in the gas reservoir 4.

An exemplary embodiment of the method for determining physical properties and/or combustion-relevant variables of a gas and Gas mixture, which is not part of the invention, is described below using Fig. 2 described. In the method, the gas or gas mixture flows under pressure through the critical nozzle 6 and via the microthermal sensor 7 into the gas reservoir 4, with the critical nozzle and the microthermal sensor being subjected to the same mass flow. The pressure increase in the gas reservoir 4 is measured as a function of time and a first gas property factor Γ*, which is dependent on a first group of physical properties of the gas or gas mixture, is determined from the measured values of the pressure increase, the first gas property factor being derived, for example, from a proportionality constant of the pressure increase . From the flow signal of the microthermal sensor 7, a second gas property factor Γ, which is dependent on a second group of physical properties of the gas or gas mixture, is determined, the second gas property factor containing, for example, the heat capacity c _p of the gas or gas mixture or being dependent on the same. Furthermore, with the help of the microthermal sensor 7, the thermal conductivity λ of the gas or gas mixture is determined and a desired physical property or combustion-relevant quantity is determined from the first and/or second gas property factor Γ*, Γ and the thermal conductivity λ by means of correlation.

Further advantageous embodiments and variants of the method can be found in previous sections of the description. The description below provides additional details about the procedure that can be used if necessary.

Advantageously, the pressure in the gas reservoir 4 is previously reduced to such an extent, for example with a vacuum pump 12, that the critical nozzle 6 can be operated critically, ie the pressure in the gas reservoir is less than half of the pressure in front of the critical nozzle. No high vacuum is required: As long as the pressure p and the temperature T in the gas reservoir 4 are measured, it can always be calculated which standard volume of gas has flowed into the gas reservoir. However, it is advantageous if the pressure is a factor lower than would be necessary for critical conditions, as the measurement can then be carried out for a correspondingly longer time, which enables a more precise determination of the proportionality constant.

For further details of the method that can be used if necessary, reference is made to the description of the first exemplary embodiment, whereby the term "pressure drop" must be replaced by "pressure increase" if necessary.

Fig. 3 shows an exemplary embodiment of a microthermal sensor for use in a measuring device, which is not part of the invention. The microthermal sensor 7 can, for example, as in Fig. 3 shown, be an integrated, microthermal CMOS hot wire anemometer, which can be arranged in a section 2 'of the measuring line and acted upon with a gas or gas mixture stream 2a. The CMOS microthermal hot wire anemometer includes a substrate 13, which typically contains a membrane 14 a few micrometers thick. The CMOS hot-wire anemometer further comprises two thermocouples 15.1, 15.2 and a heating element 16, which can be arranged between the two thermocouples in the flow direction. The two thermocouples 15.1, 15.2 can be used to record the temperature that arises due to the heat exchange 15.1a, 15.2a with the gas or gas mixture stream 2a.

For more details on how the integrated CMOS microthermal hot wire anemometer works, see D. Matter, B. Kramer, T. Kleiner, B. Sabbattini, T. Suter, "Microelectronic household gas meter with new technology", Technisches Messen 71, 3 (2004), pp. 137-146 referred.

Fig. 4 shows a representation of the directly measured density ratio ρ / ρ _ref (y-axis) as a function of the correlated density ratio ρ _corr / ρ _ref (x-axis) for different gas groups at standard conditions (0 ° C, 1013.25 mbar), whereby the correlated density ratio with was determined using a method or a measuring device according to the present invention. A typical H natural gas was used as the reference gas.

The measuring device described above for determining physical properties and/or combustion-relevant variables of a gas and gas mixture is to be assigned to a new category, namely "measuring the pressure drop or increase in pressure in a gas reservoir, where the gas flows through a critical nozzle, as well as thermal conductivity and flow measurement using a microthermal sensor, and data validation by summing the flow values". The components used are inexpensive, which allows new markets to be opened up in which gas quality sensors are not used today due to cost reasons In terms of accuracy, little loss is to be expected compared to more expensive, commercially available devices, since at least three independent measured values are used for the correlation.

In a second embodiment, the invention includes the use of a gas reservoir and a critical nozzle for determining physical properties and/or combustion-relevant variables of a gas or gas mixture, or a method in which a gas reservoir and a critical nozzle are used to determine physical properties and/or Combustion-relevant variables of a gas or gas mixture are used, the gas or gas mixture flowing under pressure from the gas reservoir through the critical nozzle, the pressure drop in the gas reservoir being measured as a function of time, from the measured values of the pressure drop one of physical properties of the gas or Gas mixture-dependent gas property factor Γ* is determined, which is derived, for example, from a time constant of the pressure drop, and from the gas property factor Γ* a desired physical property or combustion-relevant quantity is determined by means of correlation.

Fig. 5a shows an exemplary embodiment of the schematic structure of a measuring device according to the second embodiment of the invention in the case in which the gas main line 1 has a pressure that is higher than the critical pressure for the critical nozzle 6 of the measuring device (high-pressure variant). In the exemplary embodiment, the measuring device comprises, in addition to the critical nozzle 6, an evaluation unit 11 which is used to carry out a method according to the second embodiment of the invention is set up, and a gas reservoir 4, which is provided with a pressure sensor 8, the gas reservoir 4 being connected to the critical nozzle 6 for measurement.

If necessary, the measuring device can additionally contain one or more of the following components: a measuring line 2, which leads to the gas reservoir 4, and which can be connected to a main gas line 1 during operation, an inlet valve 3, which can be arranged in the measuring line 2, in order to to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir, in order to control the gas flow from the gas reservoir, an outlet 10, in order to remove the gas flowing out of the measuring device, an additional pressure sensor 8 ', which is at the outlet 10 can be arranged, a temperature sensor 9, which is arranged in the gas reservoir, and a compressor 12 ', which can be arranged on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

An exemplary embodiment of the method for determining physical properties and/or combustion-relevant variables of a gas or gas mixture according to the second embodiment of the invention is described below with reference to Fig. 5a described. In this exemplary embodiment, the gas or gas mixture flows from the gas reservoir 4 through the critical nozzle 6. The pressure drop in the gas reservoir 4 is measured as a function of time and the measured values of the pressure drop are used to calculate a gas property factor F* that is dependent on a group of physical properties of the gas or gas mixture. determined, whereby the gas property factor is derived, for example, from a time constant of the pressure drop. Furthermore, a desired physical property or combustion-relevant quantity is determined from the gas property factor Γ* by means of correlation.

Advantageously, with the second embodiment of the invention, binary gas mixtures are analyzed for their proportion of the two components forming the gas mixture, since the gas property factor Γ* is intrinsically a continuous function of the gas proportions x% or (1-x%). With knowledge of the proportion x% or (1-x%), physical properties can then be calculated from tables or using appropriate calculation programs and/or combustion-relevant size of the binary gas mixture can be determined. Of course, the direct correlation of these physical properties and/or combustion-relevant size of the binary gas mixture with the gas property factor Γ* is also possible.

In one embodiment variant of the method, the percentage share of one component in a binary gas mixture is thus determined, with the quantity to be correlated either corresponding to the composition share of the one component (x%) and/or any other physical property of the binary gas mixture.

Further advantageous embodiments and variants of the method can be found in previous sections of the description. The description below provides additional details about the procedure that can be used if necessary.

Advantageously, the inlet valve 3 and outlet valve 5 are first opened in order to allow the gas or gas mixture to be measured to flow from the main gas line 1 via the measuring line 2 through the measuring device, which can ensure that there is no longer any foreign gas from the last measurement in the measuring device . The inlet valve and outlet valve can be opened via a control unit. In some cases, the evaluation unit 11 can also be used, as in Fig. 5a shown, take over control of the inlet valve and exhaust valve. Then the outlet valve 5 is closed and the gas reservoir 4, whose volume V is known, fills until the inlet valve 3 is closed. Pressure p and temperature T in the gas reservoir can be measured with the pressure sensor 8 or temperature sensor 9, so that the standard volume V _norm of the gas or gas mixture located in the gas reservoir 4 can be determined at any time. $$v_{\mathit{standard}}=\frac{p}{1013.25\mathit{mbar}}\cdot \frac{273.15K}{T}\cdot v.$$

If the pressure p in the gas reservoir 4 is greater than the pressure p _crit , which is required so that the nozzle 6 can be operated critically, the outlet valve 5 can be opened again. Preferably, the pressure p in the gas reservoir is several bar higher than p _crit , so that the pressure drop measurement can be carried out over this range of pressure increase without the nozzle 6 no longer being operated critically. Now the outlet valve 5 is closed again, which ends the pressure drop measurement. The pressure sensor 8 is preferably designed as a differential pressure sensor relative to the outlet 10 of the measuring device. However, it is also possible to provide an additional pressure sensor 8' at the outlet.

During the pressure drop measurement, the time-dependent pressure p(t) and the time-dependent temperature T(t) in the pressure reservoir 4 were measured and recorded by the evaluation unit 11. With this data, the time constant τ in equation (6) or the proportionality constant in equation (6') and the gas property factor Γ* in equation (7) or (7') are determined in the evaluation unit.

In the evaluation unit 11, depending on the desired, combustion-relevant quantity Q, the calculation is now carried out using equation (15) with the previously determined correlation function Q _corr = f _corr (Γ*).

If necessary, you can also, as in Fig. 5b shown, a compressor 12 'may be provided, which is arranged, for example, on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

Fig. 6 shows a second exemplary embodiment of the schematic structure of a measuring device according to the second embodiment of the invention, in which a negative pressure is used in the gas reservoir. This so-called low-pressure variant is advantageous, for example, when supplying gas to end customers. In the second exemplary embodiment, the measuring device comprises, in addition to the gas reservoir 4, a pressure sensor 8, with which the gas reservoir is provided, an evaluation unit 11, which is set up to carry out a method according to the second embodiment of the invention, and a critical nozzle 6, the gas reservoir 4 for the measurement is connected to the critical nozzle 6.

If necessary, the measuring device can additionally contain one or more of the following components: a vacuum pump 12, which is connected to the gas reservoir 4 in order to generate a negative pressure in the gas reservoir, a measuring line 2, which leads to the gas reservoir 4, and which, in operation, with a Main gas line 1 can be connected, an inlet valve 3, which can be arranged in the measuring line 2 in order to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir in order to control the gas flow from the gas reservoir, an outlet 10 to remove the gas flowing out of the measuring device, an additional pressure sensor 8 ', which can be arranged in the measuring line 2 or gas main line, and a temperature sensor 9, which is arranged in the gas reservoir 4.

A further exemplary embodiment of the method for determining physical properties and/or combustion-relevant variables of a gas and gas mixture according to the second embodiment of the invention is described below with reference to Fig. 6 described. In this exemplary embodiment, the gas or gas mixture flows under pressure through the critical nozzle 6 into the gas reservoir 4. The pressure increase in the gas reservoir 4 is measured as a function of time and the measured values of the pressure increase are used to create a gas property factor that is dependent on a group of physical properties of the gas or gas mixture Γ* is determined, whereby the gas property factor is derived, for example, from a proportionality constant of the pressure increase. From the gas property factor Γ*, a desired physical property or variable relevant to combustion is determined by means of correlation.

Further advantageous embodiments and variants of the method can be found in previous sections of the description. The description below provides additional details about the procedure that can be used if necessary.

Advantageously, the pressure in the gas reservoir 4 is previously reduced to such an extent, for example with a vacuum pump 12, that the critical nozzle 6 can be operated critically, ie the pressure in the gas reservoir is less than half of the pressure in front of the critical nozzle. It's not high vacuum Required: As long as the pressure p and the temperature T in the gas reservoir 4 are measured, it can always be calculated which standard volume of gas has flowed into the gas reservoir. However, it is advantageous if the pressure is a factor lower than would be necessary for critical conditions, as the measurement can then be carried out for a correspondingly longer time, which enables a more precise determination of the proportionality constant.

For further details of the method that can be used if necessary, reference is made to the description of the first exemplary embodiment, whereby the term "pressure drop" must be replaced by "pressure increase" if necessary.

Fig. 7 shows a representation of the directly measured methane content n _CH4 (y-axis) as a function of the correlated methane content n _{CH4 corr} (x-axis) for a binary raw biogas consisting of methane and carbon dioxide under standard conditions (0 ° C, 1013.25 mbar), wherein the correlated methane content was determined using a method or a measuring device according to the second embodiment of the invention. A typical H natural gas was used as the reference gas. The desired quantity Q (here the methane content n _{CH4 corr} in x%) is advantageously determined using the correlation function Q _corr = a + b · Γ* + c · Γ* ² + d · Γ* ³ , whereby in the figure shown Example numerically a = -7.82, b = 22.7, c = -20.4 and d = 6.45.

The measuring device described above for determining physical properties and/or combustion-relevant variables of a gas and gas mixture is to be assigned to a new category, namely "measuring the pressure drop or increase in pressure in a gas reservoir, with the gas flowing through a critical nozzle. The components used are cost-effective, which makes it possible to open up new markets in which gas quality sensors are not used today due to cost reasons. In terms of accuracy, certain losses are to be expected compared to more expensive, commercially available devices, since only one independent measured value is used for the correlation instead of three.

bestimmt wird, in dem $v_x^{\prime }$

die aus dem ausgeflossenen Gasvolumen bestimmte Fliessgeschwindigkeit bezeichnet, und aus dem Gaseigenschaftsfaktor, der zum Beispiel durch $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

gegeben sein kann (siehe Gleichung (9)), mittels Korrelation eine gesuchte physikalische Eigenschaft oder brenntechnisch relevante Grösse ermittelt wird.In addition, in a third embodiment, the invention includes the use of a gas reservoir and a microthermal sensor calibrated for a specific calibration gas or gas mixture for determining physical properties and/or combustion-relevant variables of a gas or gas mixture, or a method in which a gas reservoir and a Microthermal sensor calibrated for a specific calibration gas or gas mixture can be used to determine physical properties and / or combustion-relevant variables of a gas or gas mixture, the gas or gas mixture flowing under pressure from the gas reservoir over the microthermal sensor, with the one for a specific Calibration gas or gas mixture calibrated microthermal sensor certain volume flow _v $S/v_x^{\prime }$

is determined in which $v_x^{\prime }$

denotes the flow velocity determined from the gas volume that has flowed out, and from the gas property factor, which is determined, for example, by $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

can be given (see equation (9)), a desired physical property or combustion-relevant quantity is determined by means of correlation.

The third embodiment of the invention described above can also be viewed as an independent invention.

Fig. 8a shows an exemplary embodiment of the schematic structure of a measuring device according to the third embodiment, which is not part of the invention, in the case in which the gas main line 1 is under pressure (high-pressure variant). In the exemplary embodiment, the measuring device comprises an evaluation unit 11, which is set up to carry out a method according to the third embodiment of the invention, a gas reservoir 4, which is provided with a pressure sensor 8, and a microthermal sensor 7 for measuring the flow and thermal conductivity, whereby the Gas reservoir 4 is connected to the microthermal sensor 7 for the measurement.

If necessary, the measuring device can additionally contain one or more of the following components: a measuring line 2, which leads to the gas reservoir 4 leads, and which can be connected during operation to a main gas line 1, an inlet valve 3, which can be arranged in the measuring line 2 to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir to control the gas flow from the gas reservoir, an outlet 10 for discharging the gas flowing out of the measuring device, an additional pressure sensor 8 ', which can be arranged at the outlet 10, a temperature sensor 9, which is arranged in the gas reservoir, and a compressor 12', which can be arranged on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

bestimmt wird, in dem $v_x^{\prime }$

die aus dem ausgeflossenen Gasvolumen bestimmte Fliessgeschwindigkeit bezeichnet, und aus dem Gaseigenschaftsfaktor, der zum Beispiel durch $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

gegeben sein kann (siehe Gleichung (9)), mittels Korrelation eine gesuchte physikalische Eigenschaft oder brenntechnisch relevante Grösse ermittelt wird.An exemplary embodiment of the method for determining physical properties and/or combustion-relevant variables of a gas and gas mixture according to the third embodiment, which is not part of the invention, is described below with reference to Fig. 8a described. In the method, the gas or gas mixture flows under pressure from the gas reservoir 4 via the microthermal sensor 7 calibrated for a specific calibration gas or gas mixture, the volume flow v _x A being summed up and compared with the gas volume flowing out of the gas reservoir, from the comparison of the two volumes is a gas property factor that depends on the physical properties of the gas or gas mixture $S/v_x^{\prime }$

is determined in which $v_x^{\prime }$

denotes the flow velocity determined from the gas volume that has flowed out, and from the gas property factor, which is determined, for example, by $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

can be given (see equation (9)), a desired physical property or combustion-relevant quantity is determined by means of correlation.

In an advantageous embodiment of the method, the thermal conductivity λ of the gas or gas mixture is additionally determined with the aid of the microthermal sensor 7.

gegeben sein kann (siehe Gleichung (9)), dem Kehrwert der Wärmediffusivität des Gasgemisches entspricht, anhand derer zusammen mit der Wärmeleitfähigkeit λ, die mit dem mikrothermischen Sensor separat gemessen werden kann, eine Unterscheidung der H- bzw. L-Gasgruppe möglich wird.Advantageously, with the third embodiment, which is not part of the invention, natural gas mixtures are examined to determine whether they belong to the H gases or L gases (gases with a high (high) or low (low) calorific value), since the gas property factor for example through $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

can be given (see equation (9)), the reciprocal of the heat diffusivity of Gas mixture corresponds, which, together with the thermal conductivity λ , which can be measured separately with the microthermal sensor, makes it possible to distinguish between the H and L gas groups.

) mit dem Kehrwert der Wärmediffusivität c_p·ρ/λ identifiziert wird, und indem bei gegebener Wärmeleitfähigkeit die Zuteilung anhand eines Grenzwerts für die Wärmediffusivität erfolgt, oberhalb dessen ein Gasgemisch als L-Gas und unterhalb dessen als H-Gas klassifiziert wird.The class affiliation of a natural gas mixture to the H or L gas group can be determined, for example, by using the gas property factor ( $S/v_x^{\prime }$

) is identified with the reciprocal of the heat diffusivity c _p ·ρ / λ , and in that, for a given thermal conductivity, the allocation is made based on a limit value for the heat diffusivity, above which a gas mixture is classified as L gas and below which as H gas.

eine Einteilung des gemessenen Gases in H- beziehungsweise L-Gas vorgenommen.In one embodiment variant of the method, the thermal conductivity λ of the gas or gas mixture is additionally determined with the help of the microthermal sensor 7 and together with the gas property factor $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

the measured gas is divided into H or L gas.

Further advantageous embodiments and variants of the method can be found in previous sections of the description. The description below provides additional details about the procedure that can be used if necessary.

Advantageously, the inlet valve 3 and outlet valve 5 are first opened in order to allow the gas or gas mixture to be measured to flow from the main gas line 1 via the measuring line 2 through the measuring device, which can ensure that there is no longer any foreign gas from the last measurement in the measuring device . The inlet valve and outlet valve can be opened via a control unit. In some cases, the evaluation unit 11 can also be used, as in Fig. 8a shown, take over control of the inlet valve and exhaust valve. Then the outlet valve 5 is closed and the gas reservoir 4, whose volume V is known, fills until the inlet valve 3 is closed. Pressure p and temperature T in the gas reservoir can be measured with the pressure sensor 8 and temperature sensor 9, respectively, so that at any time the standard volume V _norm of the gas or gas mixture located in the gas reservoir 4 can be concluded. $$v_{\mathit{standard}}=\frac{p}{1013.25\mathit{mbar}}\cdot \frac{273.15K}{T}\cdot v.$$

Now the outlet valve 5 can be opened again. Preferably, the pressure p in the gas reservoir 4 is so much higher than the pressure downstream of the gas reservoir that the time period in which the gas flows from the gas reservoir 4 via the microthermal sensor 7 is long enough to measure the volume flow v _x A with sufficient accuracy to be able to add up. Now the outlet valve 5 is closed again, which ends the flow measurement. The pressure sensor 8 is preferably designed as a differential pressure sensor relative to the outlet 10 of the measuring device. However, it is also possible to provide an additional pressure sensor 8' at the outlet.

During the flow measurement, flow data was measured with the microthermal sensor 7 and recorded by the evaluation unit 11 in order to determine the factor S in equation (9). Since the inlet and outlet valves are closed after the flow measurement, gas no longer flows through the microthermal sensor 7. The thermal conductivity measurement λ can now be measured. Again recorded by the evaluation unit, the thermal conductivity λ is determined using the solution to equation (12).

bestimmt wird, in dem $v_x^{\prime }$

die aus dem ausgeflossenen Gasvolumen bestimmte Fliessgeschwindigkeit bezeichnet. Zweckmässigerweise werden die Volumina für den Vergleich mittels Gleichung (17) auf Normbedingungen umgerechnet, so dass $v_x^{\prime }$

durch $${\mathrm{v}}_{\mathrm{x}}^{\prime }={\mathrm{v}}_{\mathrm{x}}\cdot V_{\mathit{diff}}^{\mathit{norm}}/V_{\mathit{sum}}^{\mathit{norm}}$$

gegeben ist mit dem auf Normbedingungen umgerechneten, ausgeflossenen Gasvolumen $V_{\mathit{diff}}^{\mathit{norm}}$

und dem auf Normbedingungen umgerechneten, aufsummierten Volumen $V_{\mathit{sum}}^{\mathit{norm}}$

. Danach, je nach gewünschter, brenntechnisch relevanter Grösse Q, erfolgt nun in der Auswerteeinheit 11 deren Berechnung anhand der Gleichung (15) mit zuvor ermittelter Korrelationsfunktion $Q_{\mathit{corr}}={ƒ}_{\mathit{corr}}\left(S/\mathrm{v}{\prime }_{\mathrm{x}}\right)$

oder der Wert von $S/v_x^{\prime }$

wird dazu benutzt, um zusammen mit der Wärmeleitfähigkeit λ ein Erdgasgemisch der Kategorie H-bzw. L-Gas zuzuordnen.With this data, the volume flow is added up to the volume V _sum in the evaluation unit 11 and compared with the gas volume V _diff flowing out of the gas reservoir. By comparing the two volumes, a gas property factor that depends on the physical properties of the gas or gas mixture can now be derived $S/v_x^{\prime }$

is determined in which $v_x^{\prime }$

denotes the flow velocity determined from the gas volume that has flowed out. The volumes for the comparison are expediently converted to standard conditions using equation (17), so that $v_x^{\prime }$

through $${\mathrm{v}}_{\mathrm{x}}^{\prime }={\mathrm{v}}_{\mathrm{x}}\cdot v_{\mathit{diff}}^{\mathit{standard}}/v_{\mathit{sum}}^{\mathit{standard}}$$

is given by the outflowed gas volume converted to standard conditions $v_{\mathit{diff}}^{\mathit{standard}}$

and the summed volume converted to standard conditions $v_{\mathit{sum}}^{\mathit{standard}}$

. Then, depending on the desired, combustion-relevant quantity Q, its calculation is carried out in the evaluation unit 11 using equation (15) with a previously determined correlation function $Q_{\mathit{corr}}={ƒ}_{\mathit{corr}}\left(S/\mathrm{v}{\prime }_{\mathrm{x}}\right)$

or the value of $S/v_x^{\prime }$

is used, together with the thermal conductivity λ, to create a natural gas mixture of the H or assigned to L-gas.

If necessary, you can also, as in Fig. 8b shown, a compressor 12 'may be provided, which is arranged, for example, on the inlet side of the gas reservoir 4 in order to increase the pressure in the gas reservoir.

Fig. 9 shows a second exemplary embodiment of the schematic structure of a measuring device according to the third embodiment, which is not part of the invention, in which a negative pressure is used in the gas reservoir. This so-called low-pressure variant is advantageous, for example, when supplying gas to end customers. In the second exemplary embodiment, the measuring device comprises, in addition to the gas reservoir 4, a pressure sensor 8 with which the gas reservoir is provided, an evaluation unit 11 which is set up to carry out a method according to the third embodiment, which is not part of the invention, and a microthermal sensor 7 for Measurement of the flow and thermal conductivity, the gas reservoir 4 being connected to the microthermal sensor 7 for the measurement.

If necessary, the measuring device can additionally contain one or more of the following components: a vacuum pump 12, which is connected to the gas reservoir 4 in order to generate a negative pressure in the gas reservoir, a measuring line 2, which leads to the gas reservoir 4, and which, in operation, with a Main gas line 1 can be connected, an inlet valve 3, which can be arranged in the measuring line 2 in order to control the gas supply to the gas reservoir, an outlet valve 5, which is arranged on the outlet side of the gas reservoir in order to control the gas flow from the gas reservoir control, an outlet 10 to remove the gas flowing out of the measuring device, an additional pressure sensor 8 ', which can be arranged in the measuring line 2 or gas main line, and a temperature sensor 9, which is arranged in the gas reservoir 4.

bestimmt, in dem $v_x^{\prime }$

die aus dem ausgeflossenen Gasvolumen bestimmte Fliessgeschwindigkeit bezeichnet, und aus dem Gaseigenschaftsfaktor, der zum Beispiel durch $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

gegeben sein kann (siehe Gleichung (9)), mittels Korrelation eine gesuchte physikalische Eigenschaft oder brenntechnisch relevante Grösse ermittelt.A further exemplary embodiment of the method for determining physical properties and/or combustion-relevant variables of a gas and gas mixture according to the third, which is not part of the invention, is described below with reference to Fig. 9 described. In this exemplary embodiment, the gas or gas mixture flows under a pressure that is typically so much higher than the pressure after the gas reservoir that the period of time in which the gas flows from the gas reservoir 4 over the microthermal sensor 7 is long enough to maintain the volume flow v _x ·A to be able to sum up with sufficient precision. The summed volume flow V _sum is compared with the gas volume V _diff that flowed out of the gas reservoir, and from the comparison of the two volumes a gas property factor is derived that is dependent on the physical properties of the gas or gas mixture $S/v_x^{\prime }$

determined in which $v_x^{\prime }$

denotes the flow velocity determined from the gas volume that has flowed out, and from the gas property factor, which is determined, for example, by $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

can be given (see equation (9)), a desired physical property or combustion-relevant variable is determined by means of correlation.

eine Einteilung des gemessenen Gases in H- beziehungsweise L-Gas vorgenommen.In an advantageous embodiment of the method, the thermal conductivity λ of the gas or gas mixture is determined with the help of the microthermal sensor 7 and, for example, together with the gas property factor $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

the measured gas is divided into H or L gas.

For further advantageous embodiments and variants of the method and for details of the method that can be used if necessary, reference is made to the previous sections of the description, whereby the term "pressure drop" must be replaced by "pressure increase" if necessary.

im Wesentlichen der Kehrwert der Wärmediffusivität des Gasgemisches ist, kann demnach mit zusätzlich gemessener Wärmeleitfähigkeit λ die Unterscheidung H- bzw. L-Gas getroffen werden. Alle Werte sind bei Normbedingungen (0°C, 1013.25 mbar) gezeigt. Als Referenzgas wurde ein typisches H-Erdgas verwendet (gestrichelte Linie bei der Koordinate (1.00,1.00). Fig. 10 shows a representation of how a distinction can be made between H and L gas based on known thermal conductivities λ (x-axis) and thermal diffusivities λ/(c _p ρ), also called thermal conductivities, (y-axis). L gases above the H/L gas separation line typically have higher heat diffusivities than H gases with the same thermal conductivity below the separation line (double arrow at x ≈1.024). Since the gas property factor $S/v_x^{\prime }=c_p\cdot \rho /\lambda$

is essentially the reciprocal of the heat diffusivity of the gas mixture, the distinction between H and L gas can be made with additionally measured thermal conductivity λ. All values are shown under standard conditions (0°C, 1013.25 mbar). A typical H natural gas was used as the reference gas (dashed line at the coordinate (1.00,1.00).

The measuring device described above for determining physical properties and/or combustion-relevant variables of a gas and gas mixture is to be assigned to a new category, namely "thermal conductivity and flow measurement using a microthermal sensor, adding up the flow values and comparing them with a volume outflow from a reference volume. Allocation of natural gases to the H-Gas or L-Gas group. The components used are inexpensive, which makes it possible to open up new markets in which gas quality sensors are not currently used due to cost reasons. In terms of accuracy, little loss is to be expected compared to more expensive, commercially available devices, since two independent measured values are used for the correlation instead of three.

Claims (7)

1. Use of a gas reservoir (4) and a critical nozzle (6) for determining physical properties and/or combustion-relevant quantities of a gas or gas mixture, wherein:

   - the gas or gas mixture flows under pressure from the gas reservoir (4) through the critical nozzle (6);

   - the pressure drop in the gas reservoir (4) is measured as a function of time;

   - a gas property factor (Γ*) dependent on physical properties of the gas or gas mixture is determined from the measured values of the pressure drop, which is derived from a time constant of the pressure drop, wherein an exponential drop of the measured pressure is assumed; and

   - a desired physical property or combustion-relevant quantity is determined from the gas property factor (Γ*) by means of correlation.
2. A method according to claim 1, in which the percentage of the one component is determined in a binary gas mixture, wherein the variable to be correlated corresponds either to the composition percentage of the one component (x%) and/or to any other physical property of the binary gas mixture.
3. The method according to any one of the preceding claims, in which binary gas mixtures are analyzed for their content of the two components forming the gas mixture, wherein the gas property factor (Γ*) is intrinsically a continuous function of the gas content (x% or 1-x%), and with knowledge of the gas content (x% or 1-x%), physical properties and/or combustion-relevant quantities of the binary gas mixture are subsequently determined from sets of tables or by means of corresponding calculation programs.
4. The method according to any one of the preceding claims, wherein the desired physical property is the density or the thermal conductivity or the heat capacity or the viscosity of the gas or gas mixture, and/or wherein the combustion-relevant quantity is the energy content or the calorific value or the Wobbe index or the methane number or the air requirement of the gas or gas mixture.
5. The method according to any one of the preceding claims, wherein the desired physical property or combustion-relevant quantity (Q) is determined by means of a correlation function Q_corr = a + b· Γ* + c · - Γ*² + d · Γ*³, wherein a, b, c, and d are constants.
6. A measuring device for determining physical properties and/or combustion-relevant quantities of a gas or gas mixture, having an evaluation unit (11) which is equipped for carrying out a method according to any one of the claims 1 to 5, and having a critical nozzle (6) and a gas reservoir (4) which is provided with a pressure sensor (8), wherein the gas reservoir is connected to the critical nozzle for the measurement.
7. The measuring device according to claim 6 additionally comprising a compressor (12') to increase the pressure in the gas reservoir or a vacuum pump (12) which is connected to the gas reservoir (4) to generate a negative pressure in the gas reservoir.

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